The invention relates to a method for monitoring the operation on the intake-manifold flap for switching over the intake manifold in an internal combustion engine.
In specific rpm ranges, resonances of the air column occur in the intake manifold of an engine which can be used for an improved air charge of the cylinder. To achieve this effect in other rpm ranges, it has been long known to change the length of the intake manifold by switching over an intake-manifold flap mounted in the intake manifold. At other rpms, resonances occur in the air column in the intake pipe by changing the length of the intake manifold and can be used at these rpms to improve the air charge to the cylinders.
It is known to change the geometry of the intake manifold to achieve optimal low speed torque and high rated output at maximum engine speed. In this connection, reference can be made to the text entitled xe2x80x9cAutomotive Handbookxe2x80x9d published by Robert Bosch GmbH, pages 476 and 477 (1996). An arrangement for continuously changing the length of an air-intake manifold of an internal combustion engine is also disclosed in German patent publication 3,608,310 (corresponding to U.S. patent application Ser. No. 07/025,548, filed Mar. 13, 1987, now abandoned). A diagnostic procedure for diagnosing the function and effect of variations of the intake manifold and the intake manifold track geometry is disclosed in U.S. Pat. No. 5,249,459, incorporated herein by reference.
The configuration and the control of an internal combustion engine having an intake-manifold switchover require an operational intake-manifold flap for switching over the intake manifold. For this reason, the limit values of the exhaust gas emission can be exceeded when there are disturbances in the operation of the intake-manifold flap.
Regulations of the California environmental authority (CARB) as well as United States federal regulations require monitoring all exhaust-gas relevant functions of a motor vehicle utilizing on-board diagnosis (OBD). The operation of the intake-manifold flap affects the exhaust gas emission values. Accordingly, it is necessary to monitor the function of the intake-manifold flap because of these regulations.
In known methods for monitoring the operation of the intake-manifold flap for switching over the intake manifold, only the output stage in a control apparatus has been monitored to date. This output stage effects the switchover of the intake-manifold flap. With this indirect monitoring, however, conclusions cannot be drawn directly as to a proper operation of the intake-manifold flap because the operation of the intake-manifold flap is not directly monitored.
It is an object of the invention to provide a method for monitoring the operation of intake-manifold flap for switching over the intake manifold of an internal combustion engine wherein a direct monitoring of the operation of the intake-manifold flap is made possible with the simplest possible technical means.
The method of the invention is for monitoring the operation of an intake-manifold flap of an intake manifold of an internal combustion engine. The intake manifold is provided to conduct an air mass flow (ms) to the cylinders of the engine and is arranged between an air intake pipe holding a throttle flap and the inlet valves of the cylinders, wherein a change of intake manifold flap position changes the resonance characteristics of the intake manifold to achieve optimal low speed torque and high rated output at maximum engine speed and the engine having an engine rpm (nmot) when running. The method includes the steps of: measuring the engine rpm (nmot) utilizing an rpm sensor; measuring the air mass flow (ms) utilizing an air mass flow sensor; computing the intake manifold pressure (ps) based on the engine rpm (nmot) and the air mass flow (ms) for at least two different intake-manifold flap positions corresponding to respectively different geometries of the intake manifold and, simultaneously, measuring the intake-manifold pressure utilizing pressure-detecting means; forming a difference between the computed and measured intake-manifold pressures for each one of at least two positions of the manifold flap; and, making a diagnosis of the operation of the intake-manifold flap by evaluating the differences formed.
A monitoring of the operation of the intake-manifold flap position for switching over the intake manifold is made possible in an especially advantageous manner by the comparison of the computed intake-manifold pressure and the measured intake-manifold pressure in dependence upon the position of the intake-manifold flap. The switchover of the intake manifold must be assumed to be defective when, during a switchover of the intake-manifold flap, in a range, in which the pressure during switchover should change significantly, a deviation of the measured pressure from the computed pressure is determined. Monitoring the operation of the position of the intake-manifold flap is possible in an especially advantageous manner by continuously monitoring the measured pressure with the aid of the computed pressure in dependence upon the position of the intake-manifold flap.
This monitoring can, for example, advantageously take place in that the differences of the computed and the measured intake-manifold pressures at different positions of the intake-manifold flap are each subtracted from each other, compared to a pregiven limit value and, when this limit value is exceeded, a fault signal is outputted.
The computation of the pressure from the air mass flow and the rpm takes place advantageously in dependence upon the intake-manifold dynamic and the position of the intake-manifold flap.
The intake-manifold dynamic considers also the following: the intake-manifold geometry as well as the position of the throttle flap, the stroke volume, the compression ratio and the degree of charge of the engine.
In an advantageous manner, factors are determined which are dependent upon the geometry of the intake manifold. These factors are determined to compute the intake-manifold pressure in dependence upon the position of the intake-manifold flap and are stored in a characteristic field.